Hydrogen is the simplest and most abundant element in the universe. Hydrogen-based energy is considered the cleanest of the currently known energy sources. Hydrogen fuel cells are expected to be applied widely to various industries in the future since they may harness the chemical energy of hydrogen to generate electricity without combustion or pollution. Hydrogen storage, however, has been a major bottleneck for long time. Currently, there are only four major systems for hydrogen storage [1, 2]: liquid hydrogen, compressed hydrogen gas, cryo-adsorption system, and metal hydride systems [3]. On the one hand, hydrogen's great asset as a renewable energy carrier is that it is storable and transportable. On the other hand, its very low natural density requires storage volumes that still are impractical for vehicles and many other uses. Current practice has been focused on compressing the gas in pressurized tanks, but this still provides only limited driving range for vehicles and is bulkier than desirable for other uses as well. It also has been found that liquefying the hydrogen more than doubles the fuel density, but uses up substantial amounts of energy to lower the temperature sufficiently (−253° C. at atmospheric pressure), requires expensive insulated tanks to maintain that temperature, and still falls short of desired driving range. One possible way has been tried to store hydrogen at higher density is in the spaces within the crystalline structure of metal hydrides. Heat then releases the hydrogen for use. Thus far, however, densities are still not high enough and costs are high.
It is well known that porous carbon powder is able to adsorb neutral hydrogen molecules in its microscopic pores. The main problems are that high pressures must be applied in order to get the neutral hydrogen molecules into the pores. About 5.2 wt % of hydrogen adsorbed into the activated carbon has been achieved at cryogenic temperatures and at pressures of about 45-60 bar [5, 6]. At ambient temperatures and at a pressure of 60 atm the adsorption figure has been only approximately 0.5 wt % [4-14], and unfortunately this method does not meet the target values of 6.5 wt % established by the U.S. Department of Energy (DOE) hydrogen storage for needs of automotive industry.
Electronegative gases and plasmas currently have attracted attention mainly in applications related to surface processing, atmospheric science, environmental studies for disposal gas cleaning and many others. Therefore there are many situations in contemporary plasma physics in which the role of negative ions is significant. The fundamental properties of negative ions have been extensively studied [15, 16 and 17]. Electronegative plasmas are also commonly used for the generation of negative ion beams [18]. The technique of ionization of hydrogen is based on utilization of the gas discharge plasma. Gas discharge plasma is an active and dynamic medium. The plasma can be understood as a partly ionized gas, where a certain part of the gas atoms or molecules are ionized to form ions under simultaneous production of electrons. Being charged, these items interact with each other. Interaction with electromagnetic fields leads to the exertion of forces acting on molecular or atomic particles. The plasma requires a continuous supply of power. The system transferring power into the gas for the ionization process constitutes the plasma source. Besides the charged particles, the plasma also comprises neutral particles having their inner electronic states changed (excited particles) or having an enhanced chemical reactivity (dissociated molecules, radicals). The plasma can be considered a dynamic system of the generation and decay of charged and activated species.
A corona is a process by which a current develops from an electrode with a high potential in a neutral fluid, e.g., hydrogen or oxygen, by ionizing the fluid so as to create plasma around the electrodes. The ions generated eventually pass the charge to nearby areas of lower potential or recombine to form neutral gas molecules. For hydrogen gas, when the potential gradient is large enough at a point in the hydrogen fluid, the fluid at that point ionizes and it becomes conductive. If a charged object has a sharp point, the hydrogen around that point will be at a much higher gradient than elsewhere. Hydrogen near the electrode can become ionized (partially conductive), while regions more distant do not. When the hydrogen near the point becomes conductive, it has the effect of increasing the apparent size of the conductor. Since the new conductive region is less sharp, the ionization may not extend past this local region. Outside of this region of ionization and conductivity, the charged hydrogen particles slowly find their way to oppositely charged objects and are neutralized. If the geometry and gradient are such that the ionized region continues growing instead of stopping at a certain radius, a completely conductive path may be formed, resulting in a momentary spark, or a continuous arc.
Coronas may be either positive or negative. This is determined by the polarity of the voltage on the highly-curved electrode. This asymmetry is a result of the great difference in mass between electrons and positively charged or dangling-bond site ions, with only the electron having the ability to undergo a significant degree of ionizing inelastic collision at a room temperature and ordinary hydrogen pressure (e.g., 1 atm).